Full length articleFabrication of Pd-TiO2 nanotube photoactive junctions via Atomic Layer Deposition for persistent pesticide pollutants degradation
Graphical abstract
Introduction
TiO2 nanomaterials have been deeply investigated and applied in electro and photocatalytic processes for their unique semi-conductor electronic properties [[1], [2], [3]]. Nonetheless the efficient degradation of persistent organic pollutants is still challenging, and strongly depends on the surface morphological properties such as specific catalytic surface area as well as distribution and density of active sites [4,5]. The TiO2 photo-activation is regulated by its band-gap, however the main TiO2 crystalline phases used in industrial applications, rutile and anatase, present high band-gap energies of 3 and 3.2 eV, respectively [6]. These wide band-gaps require a specific UV light source to activate the electron transfer, meaning that solar light, presenting only 5% of UV radiation, cannot be exploited as a source of activation for crystalline TiO2 [[7], [8], [9]]. Upon band-gap activation, the ability to provide a high degree of control over the separation charge carriers generated on the catalyst active sites is critical to sustain and enhance the redox reactions at the catalyst/water interface [10,11].
Different strategies have been carried out to improve the catalytic efficiency of pure TiO2. Typically, TiO2 nanotubes represent an ideal candidate as a catalytic substrate given their high specific surface area [12] and fast electron transfer rate with minimal charge recombination effect provided by the well-structured vertical alignment [13]. Nevertheless, applications in catalysis are hindered by the wide bang-gap [14,15]. Pure material doping, whereby a foreign metal or non-metal atom is introduced into the matrix, is carried out on the TiO2 nanostructures to shift the absorption towards the visible light spectra [15,16]. The introduction of the doping agent into the matrix requires however post-synthesis treatments such as plasma doping, ion implantation or, thermal annealing. These treatments may damage the TiO2 nano-architecture, resulting in loss of morphological structure such as shrinkage, sintering of adjacent nanotubes or loss in crystallinity [17,18]. Therefore requiring narrow control and limitation of the induced lattice damage [19,20].
The surface decoration of the TiO2 substrate has been considered as an alternative pathway to the doping route to improve the optical and electronic properties of the material without affecting the TiO2 lattice microstructure [21,22].
Photoactive junctions can be generated by the heterogeneous interaction with 2-D materials, such as graphene and its derivatives [23,24], or with noble metals. The design of photo-responsive junctions between semiconductors and noble metals requires however the deposition of nanoparticles (NPs) with high specific surface area and controlled morphology rather than thin coatings [[25], [26], [27]]. Specifically, noble metal NPs can enhance the optical and electronic properties upon light irradiation by exploiting the Surface Plasmon Resonance (SPR) effect [28], whereby electrons are excited and transferred at the noble metal/semi-conductor interface while the formation of a Schottky barrier prevents the charge recombination [[29], [30], [31]]. Noble metals such as Pt, Pd, Au and Ag have been investigated as particularly efficient candidates for this purpose and consequently applied in applications such as photovoltaics, H2 generation and photocatalysis [[32], [33], [34]]. Pd has gained growing attention, since it presents higher chemical stability to poisoning and corrosion than Ag [35,36] and, as Pt, possesses better thermal resistance than Au with lower risk of sintering [37,38].
Advanced nanofabrication routes are required to control the seeding of the noble nanoparticle across the surface of metal oxides, hence the interface affected by the charge transport [39]. The uniform distribution and high density of active sites, consisting of noble metal/metal oxide junctions, across the surface is critical to provide high specific surface area of catalytic sites [40,41]. The catalytic performance is directly correlated to the chemical and physical properties of the photoactive junction, therefore the deposition process is crucial to optimise size, shape and composition of the deposited nanoparticles [42,43].
Atomic Layer Deposition (ALD), a vacuum based deposition technique, has emerged as an ideal candidate to uniformly deposit NPs or thin films with controllable dimensions at the nanometre scale on challenging porous metal supports [[44], [45], [46]]. The fabrication of nano-structured catalysts by ALD offers the unique possibility of providing both homogeneous discrete dispersion and controlled particle size, hence tailoring the surface density of the catalytic active sites [47,48]. Well-organised nanoparticles can be deposited on nano-structured templates, leading to unique catalytic substrates with specific morphological aspect and interfaces [49,50]. ALD represent a scalable, rapid technology enabling the design of nanocatalysts with accurate control of distribution, size, composition and density with reduced waste and environmental impact [51,52]. This strategy is particularly attractive when considering noble metals such as Pd, since a low concentration of this expensive metal is desired to make the process cost-effective [45]. Although ALD has been used recently to prepare nanoporous noble metal-TiO2 materials for electrocatalytic applications [22,53], only a few studies are available on the potential of Pd-TiO2 nanotubes as photoactive substrates towards the degradation of POPs [54]. To this end, the impact of the morphology of Pd-TiO2 junctions and nano-interfaces on the photocatalytic activity is not yet understood and largely unexplored.
In the present work, Pd-TiO2 nanotube catalytic junctions with distinctive morphology and composition were fabricated via ALD. The physical and chemical properties of the supported Pd NPs, and therefore the catalytic interface of Pd-TiO2 junctions, were controlled by the ALD process and correlated to the catalytic performance. The impact of the SPR combined with the morphology resulting from the ALD deposition was discussed to determine the reaction mechanism occurring across the Pd-TiO2 junction. The photoenhanced degradation of 2,4 D, used as a benchmark POP, demonstrates the potential of ALD as a rising technology to manufacture nano-textured catalysts with well-defined chemical and morphological properties. The application of advanced nano-engineered materials based on Pd-TiO2 junctions can be extended from purely electro-oxidation to sun-light driven photocatalytic degradation of POPs in wastewater.
Section snippets
Materials and chemicals
Ethylene glycol (>99.8%, CAS: 107-21-1), ammonium fluoride (>99.99%, CAS: 12125-01-8), ethanol (>99.5%, CAS: 64-17-5), acetone (>99.5%, CAS: 67-64-1), palladium hexafluoroacetylacetonate (Pd(hfac)2) (CAS: 64916-48-9), formalin solution (10%, CAS: 50-00-0) were purchased from Sigma-Aldrich and used as received. Milli-Q water was used without further purification. Ti foil (thickness 0.1 mm) were purchased from GoodFellow.
Electrochemical anodization
The anodization experiments were carried out in a custom built two-electrode
Results and discussion
Different Pd-TiO2 junctions with specific morphology and interfaces were fabricated with the ALD deposition of Pd. The formation, growth and coalescence of the Pd NPs over the surface top layer of TiO2 nanotubes at different cycles were revealed from the observation of Fig. 1(A), (C) and (E). Small number of NPs exhibiting a mean diameter (D) of 5.1 nm were dispersed over the surface after 50 deposition cycles (Fig. 1(B)). The nanoparticles became larger between 50 (Fig. 1(B)) and 100 cycles (
Conclusions
The catalytic performance of Pd NPs-TiO2 nanomaterials has been investigated and discussed. The results observed showed a significant impact of the morphological, microstructural and surface chemistry of the different noble metal/semi-conductor interfaces obtained by the ALD process. The fastest degradation rate under UV–visible light and pure visible light was obtained with the Pd-TiO2 photocatalysts containing 2.7 at.% of Pd. 70% degradation of the 2,4D pesticide and 90% degradation of
Acknowledgment
This work was performed in part at the Melbourne Centre for Nanofabrication (MCN) in the Victorian Node of the Australian National Fabrication Facility (ANFF). Mr. Andrea Merenda would like to acknowledge the Australian Research Council (ARC) for funding the Linkage LP140100374 project and Dr. Ludovic Dumée also acknowledges the ARC for his DECRA DE180100130 fellowship. Mr. Andrea Merenda and Dr. Ludovic Dumée would also like to acknowledge ARC Research Hub for Energy-efficient Separation
References (106)
- et al.
TiO2 photocatalysis and related surface phenomena
Surf. Sci. Rep.
(2008) - et al.
A review on the visible light active titanium dioxide photocatalysts for environmental applications
Appl. Catal., B
(2012) - et al.
Heterogeneous photocatalytic degradation of organic contaminants over titanium dioxide: a review of fundamentals, progress and problems
J Photochem Photobiol C: Photochem Rev
(2008) - et al.
Surface modification and enhanced photocatalytic CO2 reduction performance of TiO2: A review
Appl. Surf. Sci.
(2017) - et al.
A critical review on the recent progress of synthesizing techniques and fabrication of TiO2-based nanotubes photocatalysts
Appl. Catal., A
(2014) - et al.
TiO2 nanotube layers: dose effects during nitrogen doping by ion implantation
Chem. Phys. Lett.
(2006) - et al.
Role of hydroxylation modification on the structure and property of reduced graphene oxide/TiO2 hybrids
Appl. Surf. Sci.
(2016) - et al.
Efficient removal of herbicide 2,4-dichlorophenoxyacetic acid from water using Ag/reduced graphene oxide co-decorated TiO2 nanotube arrays
J. Hazard. Mater.
(2012) - et al.
Visible-light activation of TiO2 photocatalysts: advances in theory and experiments
J Photochem Photobiol C: Photochem Rev
(2015) - et al.
A review on plasmonic metal-TiO2 composite for generation, trapping, storing and dynamic vectorial transfer of photogenerated electrons across the Schottky junction in a photocatalytic system
Appl. Surf. Sci.
(2016)
Uniform ALD deposition of Pt nanoparticles within 1D anodic TiO2 nanotubes for photocatalytic H2 generation
Electrochem. Commun.
Metal sintering mechanisms and regeneration of palladium/alumina hydrogenation catalysts
Appl. Catal., A
The influence of particle size on the catalytic properties of supported metals
Synthesis and catalytic properties of metal nanoparticles: size, shape, support, composition and oxidation state effects
Thin Solid Films
Atomic Layer Deposition (ALD): from precursors to thin film structures
Thin Solid Films
Atomic Layer Deposition of palladium films on Al2O3 surfaces
Thin Solid Films
Morphology and oxidation state of ALD-grown Pd nanoparticles on TiO2- and SrO-terminated SrTiO3 nanocuboids
Surf. Sci.
Coupling TiO2 nanotubes photoelectrode with Pd Nano-particles and reduced graphene oxide for enhanced photocatalytic decomposition of diclofenac and mechanism insights
Sep. Purif. Technol.
Situ Small angle X-ray scattering investigation of the thermal expansion and related structural information of carbon nanotube composites, Pro. Nat. Sci-Mater, 22
Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Sc, Ti, V, Cu and Zn
Appl. Surf. Sci.
Growth of g-C3N4 on mesoporous TiO2 spheres with high photocatalytic activity under visible light irradiation
Appl. Catal., B
Surface poisoning in the nucleation and growth of palladium Atomic Layer Deposition with Pd(hfac)2 and formalin
Thin Solid Films
Significance of crystallinity on the photoelectrochemical and photocatalytic activity of TiO2 nanotube arrays
Appl. Surf. Sci.
Enhancement of photocatalytic performance with the use of Noble-metal-decorated TiO2 nanocrystals as highly active catalysts for aerobic oxidation under visible-light irradiation
Appl. Catal., B
Effect of TiO2–Pd and TiO2–Ag on the photocatalytic oxidation of diclofenac, isoproturon and phenol
Chem. Eng. J.
Enhancement of photocatalytic activity by metal deposition: characterisation and photonic efficiency of Pt, Au and Pd deposited on TiO2 catalyst
Water Res.
A facile strategy to fabricate Au/TiO2 nanotubes photoelectrode with excellent photoelectrocatalytic properties
Appl. Surf. Sci.
Plasmon mediated visible light photocurrent and photoelectrochemical hydrogen generation using Au nanoparticles/TiO2 electrode
Mater. Res. Bull.
One-step synthesis of Ag@TiO2 nanoparticles for enhanced photocatalytic performance
Nanomaterials
CuO/WO3 and Pt/WO3 nanocatalysts for efficient pollutant degradation using visible light irradiation
Chem. Eng. J.
Photocatalytic degradation of various types of dyes (Alizarin S, Crocein Orange G, methyl red, Congo red, methylene blue) in water by UV-irradiated titania
Appl. Catal., B
Langmuir–Hinshelwood kinetics – a theoretical study
Catal. Commun.
Highly uniform Pt nanoparticle decoration on TiO2 nanotube arrays: a refreshable platform for methanol electrooxidation
Electrochem. Commun.
Preparation and characterization of Pt/TiO2 nanotubes catalyst for methanol electro-oxidation
Appl. Catal., B
Photocatalysis on TiO2 surfaces: principles, mechanisms, and selected results
Chem. Rev.
The electronic structure and optical response of rutile, anatase and brookite TiO2
J. Phys. Condens. Matter
Electronic and optical properties of three phases of titanium dioxide: rutile, anatase, and brookite
Phys. Rev. B
Composite Titanium Dioxide Nanomaterials
Chem. Rev.
Titanium dioxide nanomaterials: synthesis, properties, modifications, and applications
Chem. Rev.
The design, fabrication, and photocatalytic utility of nanostructured semiconductors: focus on TiO2-based nanostructures
Nanotechnol. Sci. Appl.
TiO2 nanotubes and their application in dye-sensitized solar cells
Nanoscale
Band-gap narrowing of titanium dioxide by nitrogen doping
Jpn. J. Appl. Phys.
Visible-light photocatalysis in nitrogen-doped titanium oxides
Science
Nitrogen-doped titanium dioxide as visible-light-sensitive photocatalyst: designs, developments, and prospects
Chem. Rev.
A study on the spectral photoresponse and photoelectrochemical properties of flame-annealed titania nanotube-arrays
J. Phys. D. Appl. Phys.
Doped TiO2 and TiO2 nanotubes: synthesis and applications
ChemPhysChem
Intrinsic Au decoration of growing TiO2 nanotubes and formation of a high-efficiency photocatalyst for H2 production
Adv. Mater.
Enhancement of Pd catalytic activity toward ethanol electrooxidation by Atomic Layer Deposition of SnO2 onto TiO2 nanotubes
J. Phys. Chem. C
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